Impact of Primary Safety Belt Laws on Alcohol-Related Front-Seat Occupant Fatalities: Five Case Studies

Abstract

Objective. Impaired drivers and other high-risk road users are less likely to use their safety belts, thus increasing the risk of fatal injury in the event of a crash. Although safety belt laws have been shown to increase wearing rates for daytime non-crash-involved drivers and their front-seat passengers, little evidence is available on the effect these laws have on belt usage by crash-involved drinking drivers and their passengers.

Methods. This study evaluated the influence of primary safety belt law upgrades from secondary laws on front-seat occupants of passenger cars driven by drinking drivers in fatal crashes in five states: California, Illinois, Maryland, Michigan, and Washington. The outcome measures used to evaluate these law upgrades were (1) the change in safety belt usage rates of front-seat occupants in passenger cars driven by drinking drivers in fatal crashes and (2) the change in alcohol-related front-seat occupant fatalities in passenger cars driven by drinking drivers.

Results. Four of the five states demonstrated increases in safety belt use by front-seat occupants of passenger cars of drinking drivers in fatal crashes following the upgrade to primary safety belt laws. Three states (California, Michigan, and Washington) experienced significant reductions in the number of front-seat occupant fatalities in vehicles driven by drinking drivers.

Conclusions. The adoption of primary law upgrades was associated with significant increases in safety belt use (four of five states) and significant reductions in fatalities among high-risk occupants (i.e., front-seat occupants involved in fatal crashes in vehicles driven by drinking drivers) in three of the five states studied.

Keywords:

• Safety Belt Usage
• Drinking Drivers
• Alcohol-Related Fatalities
• Fatal Crashes
• Primary Enforcement
• Safety Belt Laws
• Fatally Injured Front-Seat Occupants of Passenger Cars

ACKNOWLEDGEMENTS

This work was supported by the National Institute on Alcohol Abuse and Alcoholism (NIAAA grant number K05 AA014260) and with corporate funds from the Pacific Institute for Research and Evaluation (PIRE). It grows out of a study conducted for the National Highway Traffic Safety Administration (NHTSA), which had similar objectives (contract # DTNH22-00-H-05278). The opinions and conclusions in this article are those of the authors and not necessarily those of the sponsors.

Notes

¹ In one case (Illinois), the increase was only 9 percentage points, but a rate of 83 percent was achieved; in another case (Washington), the baseline rate was already higher than 80 percent, but an increase of 12 percentage points was achieved. We did not select Delaware or the District of Columbia for inclusion in our study (even though they achieved increases of 10+ percentage points to rates more than 80 percent) because of the small number of fatalities in these jurisdictions and the resulting instability of any changes observed.

^a Relative belt use rate as a difference and a percentage difference (alcohol-related vs. non-alcohol-related fatalities); 1-tailed test.

^b Relative belt use rate in the state adjusted by the national rate; 1-tailed test.

^a 1-tailed test (all other tests are 2-tailed).

^b Relative change in fatalities between alcohol-related and non-alcohol-related crashes adjusted by the national change.

^a Relative belt use rate as a difference and a percentage difference (alcohol-related vs. non-alcohol-related fatalities); 1-tailed test.

^b Relative belt use rate in the state adjusted by the national rate; 1-tailed test.

^a One-tailed test (all other tests are 2-tailed).

^b Relative change in fatalities between alcohol-related and non-alcohol-related crashes adjusted by the national change.

^a Relative belt use rate as a difference and a percentage difference (alcohol-related vs. non-alcohol-related fatalities); 1-tailed test.

^b Relative belt use rate in the state adjusted by the national rate; 1-tailed test.

^a One-tailed test (all other tests are 2-tailed).

^b Relative change in fatalities between alcohol-related and non-alcohol-related crashes adjusted by the national change.

^a Relative belt use rate as a difference and a percentage difference (alcohol-related vs. non-alcohol-related fatalities).

^b Relative belt use rate in the state adjusted by the national rate.

^a One-tailed test (all other tests are 2-tailed).

^b Relative change in fatalities between alcohol-related and non-alcohol-related crashes adjusted by the national change.

^a Relative belt use rate as a difference and a percentage difference (alcohol-related vs. non-alcohol-related fatalities); 1-tailed test.

^b Relative belt use rate in the state adjusted by the national rate; 1-tailed test.

^a One-tailed test (all other tests are 2-tailed).

^b Relative change in fatalities between alcohol-related and non-alcohol-related crashes adjusted by the national change.

* Statistically significant (p < .05).